The AAA service in Cisco IOS 12.0 through 12.4 and 15.0 through 15.6 and IOS XE 2.1 through 3.18 and 16.2 allows remote attackers to cause a denial of service (device reload) via a failed SSH connection attempt that is mishandled during generation of an error-log message, aka Bug ID CSCuy87667.
https://ics-cert.us-cert.gov/advisories/ICSA-16-287-04
http://www.securitytracker.com/id/1036914
http://www.securityfocus.com/bid/93196
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160928-aaados